In recent years, the demand for natural gas and other gas-phase fuels has increased substantially. At the same time, stricter regulations concerning allowable levels of certain components (e.g., sulfur species, acid gases, and other compounds of environmental concern) have been imposed, prompting fuel gas producers to develop economical methods of producing a compliant gas product.
One known method of treating a gas stream to remove undesirable components is to contact the gas stream with a physical or chemical solvent. Examples of chemical solvents include amines such as methyldiethanolamine (MDEA) and diethanolamine (DEA). Often, the selectivity of the chemical solvents can be problematic. For example, while amines are capable of efficiently removing hydrogen sulfide (H2S) from gas streams, the amines are generally not capable of absorbing other undesirable sulfur-containing compounds, such as, for example carbonyl sulfide (COS). As a result, additional process steps (e.g., COS hydrolysis) must be carried out before the gas stream can be used as fuel. In addition to removing H2S, most amines also remove carbon dioxide, which can place unnecessary processing loads on subsequent waste gas facilities. Further, most processes utilizing chemical solvents require extensive cooling of the incoming gas stream and often use large volumes of stream to remove absorbed contaminants from the solvent, which make these processes energy-intensive. Physical solvent-based processes are also highly energy-intensive and often require high operating pressures and/or low operating temperatures.
It has been discovered that a sorbent can be used to treat gas streams. One example of a sorbent that can be used is a sorbent comprising zinc, a promoter metal, and silica. However, if moisture contacts the sorbent, there is a chance that silicates will form. If silicate formation cannot be controlled or at least limited, then the sorbent would lose most of its sulfur-scrubbing activity. Excessive loss of activity would necessitate frequent sorbent replacement, rendering the combined technology commercially unviable.
Accordingly, a need exists for a process for limiting the formation of silicates when using a sorbent to remove contaminants from a gas stream.